With my first attempt to use Atmel START, I tried the example project LED flasher for SAM D21 Xplained Pro. The project was created fine and exported to my PC. When I opened the project in Atmel Studio 7 and tried to build the project, the project failed to link because there was no main().

I went back to Atmel START and click on VIEW CODE. main() was in led_flasher_main.c but the file did not exist in the downloaded project folder.

I copied the text of led_flasher_main.c from Atmel START to the project folder and added to the project. The build stopped because atmel_start.h is not found.

Apparently, what exported is very different from what was in VIEW CODE.